1. Field of the Invention
The present invention relates to a drive apparatus equipped with a ball screw.
2. Description of the Prior Art
An example of this type of drive apparatus of the prior art is disclosed in Utility Model Laid-Open Publication No. 3-47787, a schematic drawing of which is shown in FIG. 1. As shown in the drawing, the drive apparatus is equipped with screw shaft 1, in which are formed two types of left and right screw grooves 1a and 1b in a state in which they are mutually intersecting. Two nuts 2 and 3 fit loosely onto the screw shaft 1 and are provided with ball circulating paths (not shown) corresponding to each of said screw grooves 1a and 1b, respectively, and a plurality of balls (not shown) are arranged and contained within the ball circulating path which circulate accompanying relative rotation of the screw shaft 1 and nuts 2 and 3.
The above-mentioned nuts 2 and 3 are able to rotate freely as a result of being supported at both ends by two ball bearings 6 and 7, respectively. Furthermore, each of the ball bearings 6 and 7 is supported by body 8a and support member 8 composed of covers 8b and 8c. In addition, in the drawing, reference numeral 9 indicates an outer ring collar which serves to prevent displacement of the outer rings of ball bearings 6 and 7.
Timing pulleys 10 and 11 are respectively fixed in the centers of the above-mentioned nuts 2 and 3. In addition, two stepping motors 13 and 14 are attached to the upper portion of support member 8 by means of attachment brackets 15 and 16, and timing pulleys 18 and 19 are fitted onto the output shafts of each of the stepping motors 13 and 14. Timing belts 21 and 22 are wrapped between mutually corresponding timing pulleys 10 and 18 and mutually corresponding timing pulleys 11 and 19, respectively.
In the drive apparatus having this constitution, as shown in the drawing, robot hand 23 to be driven is attached to the end of, for example, screw shaft 1. In this state, as a result of operating both stepping motors 13 and 14 and suitably changing the directions of rotation and rotating speeds of each nut 2 and 3, backward and forward movement, rotating movement as well as movement combining these, motions can be performed as desired with screw shaft 1, and therefore robot hand 23. The relationship of movement between nuts 2 and 3 and screw shaft 1 is as shown below.
______________________________________ Difference in No difference No difference Different rotating rotating speeds between speeds both nuts Direction of Same Opposite Same direction rotation of direction direction both nuts State of Rotation at Forward and Forward and movement of that position backward backward screw shaft movement only, movement no rotation while rotating ______________________________________
In the drive apparatus having the above-mentioned constitution, since forward and backward movement and rotating movement of robot hand 23 to be driven, along with compound movements, can be performed by only controlling the rotation of two nuts 2 and 3, the structure of the apparatus is simple, and there are many locations at which parts can be shared, thus offering the advantage of reduced costs and so forth. However, adequate results have not yet to be obtained with respect to the problem of reducing the size of the apparatus, which has recently become increasingly important.